This study represents one portion of a major program in our laboratory whose objectives are to understand the mechanisms of action involved in the selective radiosensitization of neoplastic tissues by hyperthermia. The ultimate goal of the program is to utilize this knowledge in the treatment of cancer. The objective of the present proposal is to examine the relationship between fractionated local tissue hyperthermia alone and in combination with radiation on normal tissue tolerance of the mouse. It is proposed that Phase I studies be carried out by exposing the normal tissues of the hind limb of BALB/c male mice to temperatures of 42, 43 or 44 degrees C for 15, 30 or 60 minutes for a total of 5 fractions given every 2, 3 or 4 days. Phase II studies will be carried out to evaluate the effects of fractionated heat combined with radiation on normal tissues. During and after treatment the effects of these treatments will be evaluated on hair growth, skin, muscle, muscle/nerve and bone marrow. The data on each tissue will be analyzed and evaluated as a function of time. Phase I and Phase II studies will provide information on normal tissue tolerance to heat alone or in combination with radiation which can prove useful to the oncologist.